Middle Turonion - lower Campanian carbonates in central Iraq contain estimated cumulative reserves of around 9 billion brl. More than 90% of this oil is in the Turonian Khasib Formation which forms an important reservoir at the giant East Baghdad and Baiad oilfields and also at a number of other fields in central and southern Iraq. Minor volumes of oil are present in the overlying Tanuma and Sa'di Formations. The Khasib Formation consists of limestones and marlstones containing planktonic foraminifera and calcispheres together with extensively bioturbated chalks. These sediments were laid down in a basinal to sub-basinal setting which evolved into a shallow- marine shelf or coastal lagoon. The best porosity (around 20%) occurs in the intensively bioturbated middle part of the formation, in which chalky matrix porosity is enhanced by an extensive network of micro-fractures. The Tithonion-Berriasion Chia Gara and the Valanginian-Campanian Balambo Formations are potential source rocks for this oil. Organic matter is mostly marine Type 11 kerogen or mixed marine-continental.